DATRON Multimeter - autozero fault ?

[macfly]

Hello,

after power on my old DATRON 1082 (which is nearly the same as the 106x, 107x models) never shows a 'Zero' with shorted
inputs (range set to 10V). With 'HiRes' on, it shows 10 ... 20 digits, then drifts towards zero during the next half hour, but never reaches zero exactly. I can not image, that this is the default case.

Perhaps a kind DATRON user would me tell the behaviour of his meter ... 

Regards,

macfly

 

[George Edmonds]

Hi

I have a 1065 and it does not exhibit the same behaviour as yours.

In my experience the primary problems with Datron kit are poor IC socket contacts, just reseat the IC's or bad electrolytic capacitors mainly in the power supplies.

George G6HIG.
 

[macfly]

Hi George,

thanks for you reply. I was not sure about the behaviour of my 1081, now I am.

>In my experience the primary problems with Datron kit are poor IC socket contacts, just reseat the IC's or bad electrolytic
  capacitors  mainly in the power supplies.

I have startet the refurbishing process of my 1082 a few years ago, replacing nearly all electrolytics.
The supply voltages are within their tolerance and have low ripple. But till now I will start to reseat the IC's.

Thank you!

macfly

[Gyro]

I can't remember exactly how it does the autozero now (it ought to be just be a reading offset by the micro), but it might also be one of the opto-isolators on its way out. The ones used in linear mode for compensations have been know to cause issues when their current transfer ratio drifts with age. Just a thought.

I also can't remember whether those models retain pots for input stage Vos and bias current adjustment.

[TheDefpom]

Hi George,

I have startet the refurbishing process of my 1082 a few years ago, replacing nearly all electrolytics.
The supply voltages are within their tolerance and have low ripple. But till now I will start to reseat the IC's.

Thank you!

macfly

DONT reseat the memory IC's otherwise you will lose your calibration data, all the other IC's are fine to do.

I am in the process of repairing 2 Datron 1062 units at the moment (videos will be on my channel in the near future).

A common failure is the optoisolators on the analogue board, with age their performance drops and causes issues, you can still get replacements, MCT6 and 6N136. the MCT6 are actually binned components selected for the speeds (red dot/white dot), this may or may not need to be considered when replacing them.

You will need to replace all electrolytic, they ALL fail, the ones on the analogue board are known for being a common failure, in both of my units every one of them had very bad ESR/dissipation.

[macfly]

I can't remember exactly how it does the autozero now (it ought to be just be a reading offset by the micro), but it might also be one of the opto-isolators on its way out. The ones used in linear mode for compensations have been know to cause issues when their current transfer ratio drifts with age. Just a thought.

I also can't remember whether those models retain pots for input stage Vos and bias current adjustment.

Hi Gyro.

you are right, my 1082 has three pots at the analog boards: one for offset adjust of the bootraps circuit, one for bias adjust,
and one for jitter / zero (?) adjust . These pot (R20 at the top right corner of the analog board) has direct impact at the instruments
zero point - but I think only in my case, when the autozero does not work.

EDIT: it has 4 pots, one additional for delectric absoption compensation.

Regards,

macfly

[macfly]

DONT reseat the memory IC's otherwise you will lose your calibration data, all the other IC's are fine to do.

I am in the process of repairing 2 Datron 1062 units at the moment (videos will be on my channel in the near future).

A common failure is the optoisolators on the analogue board, with age their performance drops and causes issues, you can still get replacements, MCT6 and 6N136. the MCT6 are actually binned components selected for the speeds (red dot/white dot), this may or may not need to be considered when replacing them.

You will need to replace all electrolytic, they ALL fail, the ones on the analogue board are known for being a common failure, in both of my units every one of them had very bad ESR/dissipation.

Hello TheDefpom,

I have watched the output signals of some (till now) opto couplers, but they behave as they should. One of the al-electrolytics of the +-40V charge pump was defective, but I will replace them all in the near future.

This seems not to be a common error an DATRON DMMs. I will made more measurements and hope to understand what goes wrong before replacing components.

Regards,

macfly